The use case that PulseAudio was [over]designed to fix was plugging in USB
headphones (or connecting a Bluetooth headset) and having existing audio
streams redirected there.

Please don't ever make this behavior the default!
Imagine, you have an audio setup mixing sound and pushing it out and then you plug in
some USB device that also has "audio capability" and your production sound gets
redirected there. A nightmare!

Do you really think that someone is going to be setting up an audio mixing
environment without configuring their sound setup? Or that people doing this
make up the majority of users?

Twenty years ago, very unlikely. Today, very much possible. Especially
if the behavior is not explicitly documented.

Knowing what you do and the system behaving in predictable way is one of the
beauties of UNIX and FreeBSD in particular.

I agree, however sane defaults are also very important to a useable system and
these are not mutually exclusive. It is perfectly possible to have a system
that has defaults that do what most users do (or a choice of defaults based on
a simple selection of typical uses), but which is also configurable if you have
unusual requirements. This is what we aim to do with FreeBSD.

I have no problems with the sound system supporting different setups. I
just fail to see the usefulness of such configuration, except in the
very trivial setup, where you have only one output device and add
another. What if there are three output audio devices in the systems?
Trivial with all the HDMI etc today.

An overly auto-configuring system is a pain to deal with, sometimes.
Especially if you cannot control some aspects of it's behavior. In such
cases, you end up with a more complicated setup.

Don't make it so that even idiots can use it because then, only idiots will be
using it!

This kind of argument has no place in FreeBSD. You are not a better person
because you use things that are hard to use. You are not a better person
because you choose to do things the difficult way. You are not a better person
because you prove your superiority by making life hard for others.
David